Corrugated cardboard has long been a favorite construction material of children, because of its ready availability in the form of shipping and other containers. Its ease of cutting, though often requiring adult assistance, enables use as playhouses and storage boxes for toys and other children's things. Most such containers are of a single wall thickness, i.e., a lamination of two flat sheets of kraft paper with fluted kraft paper which is cemented between the flat sheets. Some containers are of double wall thickness, being similarly constructed, but having three flat sheets with two fluted sheets between adjacent pairs of the flat sheets. Because of the added strength of the double wall board, other children's products could be made, products which were able to provide some measure of support of somewhat heavier items. However, neither single nor double wall cardboard is desirable for supporting a child's weight at least not for very long, and particularly under ordinary conditions of activity of the child.
There also exists corrugated cardboard referred to as triple wall, consisting of four flat sheets and three fluted sheets, one of each of which is sandwiched between each adjacent pair of flat sheets. This product is readily available from Tri-Wall Containers, Inc. of Butler, Ind. One use of such triple wall board is in single thickness panels (but hereinafter often referred to as sheets) for various pieces of children's furniture, e.g., stools, storage units, chairs, loungers, bookcases, desks and numerous other items. Triple wall corrugated board is immensely strong for its weight, and is about one-third the weight of plywood. Test weight for a triple wall corrugated sheet is rated at 1100 pounds.
Although triple wall corrugated board is useful to support a small child up to about five or six years of age when made into a chair, for example, the typical slotted, intersecting plane construction of the panels making up the chair makes a useful life of such a product rather limited. Depending on how the child sits, squirms or bounces in the chair and how often it is used, the expected life of even a triple wall corrugated cardboard chair is typically measurable in weeks. This is mainly due to the side thrust of the child's body against the sides of the chair, and the inability of the interrupted, relatively short joints of corrugated board to sustain such side thrust. Ordinarily, the juncture of the side panels with the seat and back panels of such a chair is the weakest point of a side panel, and this weakest point is also subjected to the greatest stress. The sides can also be subject to damage if the flutes of the sheets are vertical, since corrugated board has the greatest tendency to bend in the direction of the flutes of the board rather than across the flutes. Side thrust along the front vertical edge of the side of the chair can present a problem, since a common construction is to have the side panel slotted horizontally adjacent the front edge to receive the seat panel, leaving nothing but the strength of the panel itself to resist the lateral force from a child's thigh, for example. In most child's seat designs, the chair's weakest points are at the side panels, oftentimes at the very areas of greatest and most frequent pressures and forces from an active child.